Internal combustion engine which can be operated with a choice of different fuels, especially for a motor vehicle drive system

ABSTRACT

The invention relates to an internal combustion engine ( 1 ) which can be operated with different fuels which have different energy densities, e.g., petrol or natural gas. The invention provides that in order to balance the different output development, especially if an internal combustion engine of this type is used in the drive system of a motor vehicle, the internal combustion engine is operated with a boost in the natural gas mode. A turbo-charger ( 5 ) which is known per se or an externally driven load compressor can be used to this end. In this way, it is possible to keep the running characteristics of a motor vehicle constant, even with the use of alternative fuels with different energy densities.

[0001] The invention relates to an internal combustion engine operablealternatively on various fuels, in particular for a motor vehicle drive,said fuels having different energy densities, as for example in the caseof natural gas and gasoline.

[0002] As is known, the output of a conventional reciprocating pistonengine operating on natural gas is about 15% below that of operation ongasoline. This applies substantially throughout the output spectrum ofthe engine.

[0003] When such an internal combustion engine is employed as propulsionengine in a motor vehicle, this differential output deployment is alwaysexperienced as disagreeable by the operator when full output is calledfor, but the engine happens to be running on the fuel of low energydensity.

[0004] According to DE 195 39 170 A1, it is proposed, to remedy thisdisadvantage, that the engine be switched automatically to operation onthe fuel of higher energy density when high output is demanded, andsupplied accordingly.

[0005] However, this works only if sufficient fuel of both energydensities is available on board. If the fuel of higher energy densityhas been consumed, the output deficit cannot be made up by switching tothat kind of fuel.

[0006] The object of the present invention is to create an internalcombustion engine operable alternatively on various fuels of diverseenergy density and capable of deploying comparable constant power on thefuels available.

[0007] According to the invention, this object is accomplished in thatthe engine is equipped with a charge compressor which is switched onwhen using a fuel of low energy density, at least in event of elevatedoutput demand, so that the engine will operate as a supercharge engine,whereas the charge compressor is switched off when using the fuel ofhigh energy density.

[0008] The said charge compressor may take the form of a charge blowerdriven by a turbine driven by the exhaust gas of the engine (exhaust gasturbocharger).

[0009] Likewise, the charge compressor may be driven by the internalcombustion engine itself, or alternatively by an external drive, forexample an electric motor.

[0010] By the invention, an internal combustion engine is created that,when operated alternatively with several fuels of diverse energydensity, exhibits a nearly constant output characteristic. This is ofconsiderable importance when the internal combustion engine is employedto propel a motor vehicle, since the drivability of such a vehicleremains constant independently of the fuel used. When an automatictransmission is used in such a motor vehicle, therefore, it is notnecessary to provide different shift characteristics for the kinds offuel used from time to time.

[0011] An embodiment of the invention is described below in more detailwith reference to a drawing by way of example. The drawing shows aschematic diagram of an internal combustion engine equipped according tothe invention.

[0012] A reciprocating piston engine 1 is provided with an intake duct 2and an exhaust duct 3. In the stream of the exhaust duct 3, there is anexhaust gas turbine 4. In the stream of the intake duct 2, there is acharge blower 5. The exhaust gas turbine 4 and the charge blower 5 aremounted on a common shaft, as indicated by the dot-dash line 6, formingan exhaust gas turbocharger known per se. The exhaust gas turbine 4 isprovided with an exhaust gas by-pass line 7 in the stream of which anexhaust by-pass valve 8 is arranged. The charge blower 5 is providedwith a fresh air by-pass line 9, along which a fresh air by-pass valve10 is arranged.

[0013] A fuel tank 11 is provided to hold a liquid fuel, as for examplegasoline. This fuel tank 11 is in communication by way of a fuel line 12with a fuel proportioning system 13. From the fuel proportioning system13, another section 14 of the fuel line leads to the intake duct 2 ofthe reciprocating piston engine 1. In this section 14 of the fuel line,means 15 are provided to close and open the fuel line 11.

[0014] Further, a tank 16 is provided to hold a gaseous fuel, as forexample natural gas. This tank 16 is in communication by way of a gasline 17 with a gas proportioning system 18. From the gas proportioningsystem 18, another section 19 of the gas line leads to the intake duct 2of the piston engine 1. In this section 19 of the gas line, means 20 areprovided to close or open the gas line 17.

[0015] The means 15 and 20 are preferably embodied as electricallycontrollable valves.

[0016] Along the exhaust duct 3, downstream from the exhaust gas turbine4, there is a catalyst 21 for reduction of injurious exhaust gasconstituents.

[0017] The exhaust gas by-pass valve 8, the fresh air by-pass valve 10and the means 15, 20 provided in the fuel line 12 and the gas line 17,respectively, to close or open said lines, are controlled by anelectronic engine control system, not shown, which detects the operatingstate of the piston engine 1 by way of sensors as required from time totime.

[0018] When the piston engine 1 is to be operated on gasoline, the freshair by-pass valve 10 and the exhaust gas by-pass valve 8 are opened. Themeans 20 in the line 17 are closed. The means 15 in the fuel line 12 areopened. The piston engine 1 thus operates as a straight aspirationengine on gasoline from the fuel tank 11.

[0019] But when the piston engine is to continue operation on naturalgas, then the means 15 in the fuel line 12 are closed and the means 20in the line 17 are opened. In order to make up for the reduced output ofthe internal combustion engine in natural gas operation compared togasoline, the exhaust gas by-pass valve 8 and the fresh air by-passvalve 10 are closed. The exhaust gas turbine 4 starts and drives thecharge blower 5. As a result, the piston engine 1 is supplied with agreater charge than in aspirate operation, so that the output, despiteuse of natural gas as fuel, rises once more to the level usual ingasoline operation.

[0020] The use of such an internal combustion engine in a motor vehiclethus preserves the accustomed drivability even in alternative use ofnatural gas as fuel besides gasoline.

1. Internal combustion engine which can be run optionally on variousfuels of different energy density, in particular for a motor vehicledrive, characterised in that the engine is equipped with a superchargingcompressor which can be connected up when using a low-energy-densityfuel at least when power requirements are elevated, so that the engineworks as a supercharged engine, whereas the supercharging compressor isshut off when using a high-energy-density fuel and the engine works as anaturally aspirating engine.
 2. Internal combustion engine according toclaim 1, characterised in that the supercharging compressor is designedas a supercharger (5) driven by an exhaust turbine (4).
 3. Internalcombustion engine according to claim 1, characterised in that thesupercharging compressor is driven via a clutch directly by the engine.4. Internal combustion engine according to claim 1, characterised inthat the supercharging compressor is driven by a separate drive. 5.Internal combustion engine according to claim 4, characterised in thatthe separate drive for driving the supercharging compressor is formed byan electric motor.